1. Field of the Invention
This invention relates to a multiple contact switch with a reversible spring member curved in a predetermined direction which, upon depression, is elastically curved in the opposite direction.
2. Description of the Prior Art
It is conventional for a switch to use a reversible leaf spring so that the periphery of the reversible leaf spring is supported by a first contact in the form of a ring, and a second contact is arranged at the center of the first contact. Upon depression by a push rod, the reversible leaf spring is elastically curved downwardly to contact the second contact, so that the switch is turned on. During this operation the operator can feel the switch operate. When the pressure on the push rod is removed, the reversible leaf spring curves upwardly to its original configuration so that the switch is again turned off. Such switches are extensively employed as signal inputting means in the field of electronics.
Recently, another type of multiple contact switch has been developed in which a third contact is provided above the second contact and actuated by a push rod. The reversible leaf spring in such a switch is normally held in contact with the third contact, so that the second contact is employed as a normally-open side contact and the third contact is employed as a normally-closed side contact.
The movement of the reversible leaf spring in such a switch is extremely small, generally 0.2 to 0.3 mm. Therefore, in order to stabilize the contact pressure of the reversible leaf spring on the third contact which is the normally-closed side contact, it is necessary to assemble the switch in such a manner that the distance between the first contact and the third contact is maintained at a constant amount with extremely high accuracy. However, it is difficult for conventional manufacturing techniques to satisfy this requirement, and this makes it difficult to put such a switch into practical use.
In view of the foregoing, an object of this invention is to provide a multiple contact switch in which the contact pressure of the reversible spring member on the normally-closed side contact piece is maintained at a stable value. It is a further object to provide a switch which can be assembled readily without need for high accuracy and can, therefore, be readily put in practical use.